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See Subscription Options. Discover World-Changing Science. Mark Pagel, head of the evolutionary biology group at the University of Reading in England and editor of The Encyclopedia of Evolution , fills us in: We humans are conspicuous among the 5, or so mammal species in that we are effectively naked. Get smart. When clean-shaves were in vogue, men derived status from social approval. During beard times, manliness was about natural, physical strength.
Similarly, pubic hair practices are culturally variable. In a Cross Cultural Research study, anthropologist Peter Gray and graduate student Lyndsey Craig, both of the University of Nevada, Las Vegas, reviewed ethnographies from more than diverse societies. Of the entries that mentioned pubic hair, some groups removed it, others retained it. None of the cultures were influenced by Western pornography and marketing — the supposed drivers of removal trends in the United States.
Bridget Alex is an anthropologist and a frequent contributor to Discover. This story originally appeared in print as "Getting Naked. Register or Log In. The Magazine Shop. Login Register Stay Curious Subscribe. Planet Earth. Newsletter Sign up for our email newsletter for the latest science news. Sign Up. Chimps have more oil-secreting apocrine glands; ours occur only in a few areas of the body.
We also have 10 times more eccrine glands, the source of watery sweat. Other primates, such as these Japanese macaques, have retained the thick body fur that humans lost as we evolved to perspire more.
In the fights analyzed, beards had no effect on knockouts or wins. Sadness is referred to as "the blues". The truth may not be so far off.
Men might have beards, but compared to other mammals we're pretty bare-faced Thinkstock. Changizi, together with researchers Qiong Zhang and Shinsuke Shimojo, argues that our faces evolved their hairlessness to allow other members of our species the ability to read our emotions.
Indeed, primate faces and — in some cases — rumps and genitalia change colours thanks to the underlying physiology of the skin. Most mammals, like dogs, horses, or bears, can only see blends of two colours when they look at the world.
They're called dichromats, and they can only see yellows, blues, or the greens that form when blue and yellow mix — in addition to perceiving brightness. That's because their eyes have, in addition to the brightness-sensing rods, only two types of cones: ones sensitive to short or long wavelengths of light.
But humans and some other primates are trichromats. We have a third type of cone, sensitive to medium wavelengths of light. Having that third cone means that we can also detect colours along a red-green continuum. A few lucky people are tetrachromats , which means they can see even more shades. But there's something odd about the three types of cones that trichromats have: they're not evenly spaced out. It just so happens that this odd assortment of cones allows our eyes to perceive properties of the blood circling through our bodies just beneath the skin: how saturated with oxygen the haemoglobin is, and how concentrated the haemoglobin is.
Changes in those two variables result in predictable changes in skin colouration. The reason the rest of our body lost its fur, however, has been up for debate for decades. One popular idea that has gone in and out of favor since it was proposed is called the aquatic ape theory. The hypothesis suggests that human ancestors lived on the savannahs of Africa, gathering and hunting prey.
But during the dry season, they would move to oases and lakesides and wade into shallow waters to collect aquatic tubers, shellfish or other food sources. The hypothesis suggests that, since hair is not a very good insulator in water, our species lost our fur and developed a layer of fat. The hypothesis even suggests that we might have developed bipedalism due to its advantages when wading into shallow water.
A more widely accepted theory is that, when human ancestors moved from the cool shady forests into the savannah, they developed a new method of thermoregulation. Losing all that fur made it possible for hominins to hunt during the day in the hot grasslands without overheating. An increase in sweat glands, many more than other primates, also kept early humans on the cool side.
The development of fire and clothing meant that humans could keep cool during the day and cozy up at night. But these are not the only possibilities, and perhaps the loss of hair is due to a combination of factors. Evolutionary scientist Mark Pagel at the University of Reading has also proposed that going fur-less reduced the impact of lice and other parasites.
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